1. Field of the Invention
The present invention relates to an optical module used in an optical fiber communication.
2. Description of the Related Art
In a high-speed, large-capacity optical communication system, a wavelength division multiplex communication (D-WDM) has been adopted for the trunk line optical communication system. With this, there has been a need for an optical module in which high precision wavelength control required for the D-WDM can be realized. In the D-WDM optical module, an optical element is operated at a constant temperature using a temperature control element to suppress fluctuation in various properties of the optical element caused by environmental temperature variation.
In such an optical module, a device equipped with a Peltier element which is a temperature control element is disclosed in Japanese Laid-Open Utility Model Publication No. 62-82761 (Patent document 1). The device disclosed in Patent document 1 keeps the temperature of the laser element constant through a substrate and suppresses change in wavelength caused by temperature variation, and furthermore, maintains the change in distance between the laser element and the lens caused by external temperature variation to be small.
However, the Peltier element functions as a heat exchanger and is normally configured by sandwiching with two plates so that one surface is to be HOT and the other surface is to be COLD, where there is an inherent problem in that warp occurs due to temperature difference between the two plates in the Peltier element having a sandwich configuration with two plates.
Thus, when the Peltier element is operated, though the temperature of the optical element is kept constant, stress is applied on the optical element due to deformation of the Peltier element. The stress is also applied on the optical element due to thermal distortion or mechanical distortion of the package. When the optical element is subjected to stress, various properties of the optical element tend to change.
In the device disclosed in patent document 1, the Peltier element is arranged up to the position of a bottom surface of the substrate, corresponding to the portion for an external resonator, from the end face of the laser element to the reflection film surface of the lens, and thus stress caused by a warpage of the Peltier element is applied to the portion corresponding to the external resonator. In such configuration, the laser element and the external resonator can be operated at a constant temperature, but the stress applied to the external resonator cannot be controlled sufficiently. If the control of the stress applied to the external resonator is insufficient, the resonance wavelength changes, and high precision wavelength control cannot be expected.